Metabolically active biological materials (e.g., cells) are phenomenal biochemical catalysts capable of carrying out sequential, stereospecific biochemical reactions, and can function as sensitive biosensors. There are significant potential industrial, biomedical, and environmental uses of metabolically active biological materials. They can be used for a variety of purposes such as detecting and/or measuring the amount of an environmental contaminant, particularly metals.
Metal contamination, particularly mercury, arsenic, cadmium, chromium, and nickel contamination, continues to be a public health and environmental problem. Conventional chemical detection techniques include atomic absorption spectrophotometery, ion chromatography, gas chromatography, mass spectrometry, as well as cold-vapor atomic absorption or cold-vapor atomic fluorescence spectroscopy. At least some of these techniques can be highly sensitive but complex to perform and expensive in terms of equipment and training. Furthermore, these techniques must typically be conducted in the laboratory. Plus, these techniques do not always reflect the true biological availability of toxic metals in a system.
Microorganisms that quantitatively detect toxins in the environment offer a less expensive alternative to conventional methods. For example, microbial biosensors aimed at measuring the bioavailability of mercury have been developed as an alternative to chemical or physical analysis. U.S. Pat. No. 5,612,184 (Rosson) discloses a device for the detection of mercury in water using an aqueous suspension of recombinant biosensory microorganism cells containing a lux bioluminescence gene. The cells are bioluminescent in the presence of Hg2+ ions and/or monomethyl mercury. The resultant bioluminescence can be detected using a variety of means, e.g., photographic film, photomultiplier, photodiode, or scintillation counter. However, this patent only discloses the use of such a suspended cell biosensor for the detection of mercury in water. Furthermore, suspended cell biosensors are limited because of handling difficulties and short useful life of the cell stock solution.
Immobilization of cells for the biodetection of contaminants in aqueous environments offers advantages over the use of suspended cell systems. Immobilized cells are easy to handle, can remain viable for long periods of time, and show excellent plasmid retention. However, immobilization methods for use in biosensors have focused on reusable detection methods where the immobilized cells are used repeatedly. In such methods, control over immobilized cell stability and cell outgrowth become considerable problems together with slow biosensor response times.